Surgical navigation systems including reference and localization frames

ABSTRACT

A system for use during a medical or surgical procedure on a body. The system generates an image representing the position of one or more body elements during the procedure using scans generated by a scanner prior or during the procedure. The image data set has reference points for each of the body elements, the reference points of a particular body element having a fixed spatial relation to the particular body element. The system includes an apparatus for identifying, during the procedure, the relative position of each of the reference points of each of the body elements to be displayed. The system also includes a processor for modifying the image data set according to the identified relative position of each of the reference points during the procedure, as identified by the identifying apparatus, said processor generating a displaced image data set representing the position of the body elements during the procedure. The system also includes a display utilizing the displaced image data set generated by the processor, illustrating the relative position of the body elements during the procedure. Methods relating to the system are also disclosed. Also disclosed are devices for use with a surgical navigation system having a sensor array which is in communication with the device to identify its position. The device may be a reference frame for attachment of a body part of the patient, such as a cranial reference arc frame for attachment to the head or a spine reference arc frame for attachment to the spine. The device may also be a localization frame for positioning an instrument relative to a body part, such as a localization biopsy guide frame for positioning a biopsy needle, a localization drill guide assembly for positioning a drill bit, a localization drill yoke assembly for positioning a drill, or a ventriculostomy probe for positioning a catheter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/105,068,filed Jun. 26, 1998, now abandoned, which is a divisional of Ser. No.08/809,404, filed Mar. 21, 1997, which issued as U.S. Pat. No.6,236,875, which is a 371 of PCT/US95/12894, filed Oct. 5, 1995, whichclaims priority to Ser. No. 60/003,415, filed Sep. 8, 1995, nowabandoned, and is a continuation Ser. No. 08/319,615, filed Oct. 7,1994, now abandoned, which is a continuation-in-part of Ser. No.08/053,076, filed Apr. 26, 1993, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates generally to systems which use and generate imagesduring medical and surgical procedures, which images assist in executingthe procedures and indicate the relative position of various body partsand instruments. In particular, the invention relates to a system forgenerating images during medical and surgical procedures based on a scantaken prior to or during the procedure and based on the present positionof the body parts and instruments during the procedure.

Image guided medical and surgical procedures comprise a technology bywhich scans, obtained either pre-procedurally or intra-procedurally(i.e., prior to or during a medical or surgical procedure), are used togenerate images to guide a doctor during the procedure. The recentincrease in interest in this field is a direct result of the recentadvances in scanning technology, especially in devices using computersto generate three dimensional images of parts of the body, such ascomputed tomography (CT) or magnetic resonance imaging (MRI).

The majority of the advances in diagrammatic imaging involve deviceswhich tend to be large, encircle the body part being imaged, and areexpensive. Although the scans produced by these devices depict the bodypart under investigation with high resolution and good spatial fidelity,their cost usually precludes the dedication of a unit to be used duringthe performance of procedures. Therefore, image guided surgery isusually performed using images taken preoperatively.

The reliance upon preoperative images has focused image guidance largelyto the cranium. The skull, by encasing the brain, serves as a rigid bodywhich largely inhibits changes in anatomy between imaging and surgery.The skull also provides a relatively easy point of reference to whichfiducials or a reference system may be attached so that registration ofpre-procedural images to the procedural work space can be done simply atthe beginning, during, or throughout the procedure. Registration isdefined as the process of relating pre-procedural or intra-proceduralscan of the anatomy undergoing surgery to the surgical or medicalposition of the corresponding anatomy. For example, see Ser. No.07/909,097, now U.S. Pat. No. 5,383,454 the entire disclosure of whichis incorporated herein by reference.

This situation of rigid fixation and absence of anatomical movementbetween imaging and surgery is unique to the skull and intracranialcontents and permits a simple one-to-one registration process as shownin FIG. 1. The position during a medical procedure or surgery is inregistration with the pre-procedural image data set because of theabsence of anatomical movement from the time of the scan until the timeof the procedure; in effect, the skull and it's intracranial contentscomprise a “rigid body,” that is, an object which does not deforminternally. In almost every other part of the body there is ampleopportunity for movement within the anatomy which degrades the fidelityby which the pre-procedural scans depict the intra-procedural anatomy.Therefore, additional innovations are needed to bring image guidance tothe rest of the body beyond the cranium.

The accuracy of image guided surgery relies upon the ability to generateimages during medical and surgical procedures based on scans taken priorto or during the procedure and based on the present position and shapeof the body parts during the procedure. Two types of body parts areaddressed herein: 1) structures within the body that do not changeshape, do not compress, nor deform between the process of imaging andthe medical procedure, which are termed “rigid bodies,” and areexemplified by the bones of the skeleton; and 2) structures within thebody that can change shape and deform between the process of imaging andthe medical procedure structures are termed “semi-rigid bodies,” and areexemplified by the liver or prostate. Both types of body parts arelikely targets for medical or surgical procedures either for repair,fusion, resection, biopsy, or radiation treatment. Therefore, atechnique is needed whereby registration can be performed between thebody parts as depicted pre-procedurally on scans and the position andshape of these same body parts as detected intra-procedurally. Thistechnique must take into account that movement can occur betweenportions of the body which are not rigidly joined, such as bonesconnected by a joint, or fragments of a broken bone, and that shapedeformation can occur for semi-rigid bodies, such as the liver orprostate. In particular, the technique must be able to modify thescanned image dataset such that the modified image dataset which is usedfor localization and display, corresponds to position and/or shape ofthe body part(s) of interest during a medical or surgical procedure. Akey to achieving this correspondence is the ability to precisely detectand track the position and/or shape of the body part(s) of interestduring the medical or surgical procedure, as well as to trackinstruments, - - - or radiation used during the said procedure.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a system which allowsregistration between a body part depicted in pre-procedural images andtracked during surgery.

It is a further object of this invention to provide a system whichallows registration between a semi-rigid body such as the liver depictedin pre-procedural images and detected during surgery.

It is a further object of this invention to provide a system whichallows registration between multiple body parts such as skeletalelements depicted in pre-procedural images and detected during surgery.

It is a further object of this invention to provide a system which canlocalize a semi-rigid body that may deform between imaging and aprocedure and provide a display during the procedure of the body in itsdeformed shape.

It is a further object of this invention to provide a system which canlocalize multiple rigid bodies that move with respect to each otherbetween imaging and a procedure and provide a display during theprocedure of the bodies in their displaced positions.

It is another object of this invention to provide a system for useduring a medical or surgical procedure on the body, the systemgenerating a display representing the position of one or more bodyelements during the procedure based on a scan generated by a scannereither prior to or during the procedure.

It is another object of this invention to provide a system for useduring a medical or surgical procedure on a body which modifies the scantaken prior to or during a procedure according to the identifiedrelative position of each of the elements during the procedure.

It is another object of this invention to provide a system for useduring a medical or surgical procedure on a body which modifies theimage data set according to the identified shape of each of the elementduring the procedure.

It is another object of this invention to provide a system whichgenerates a display representative of the position of a medical orsurgical instrument in relation to the body element(s) during aprocedure.

It is a further object of this invention to provide a system for useduring image guided medical and surgical procedures which is easilyemployed by the doctor or surgeon conducting the procedure.

It is another object of this invention to provide a system whichdetermines the relative position and/or shape of body elements during amedical or surgical procedure based on the contour of the body elementswhich can avoid the need for exposing the body elements.

It is still another object of this invention to provide a system whichemploys one or more two dimensional fluoroscopic or x-ray images of bodyelements to determine their relative position and/or shape in threedimensions.

It is yet a further object of this invention to describe a surgical ormedical procedure which employs a display representing the position ofthe body element(s) during the procedure based on an image data set ofthe body element(s) generated prior to the procedure.

It is a further object of this invention to provide a system and methodfor medical or surgical procedures which allows repositioning of bodyelements during the procedure and still permits the generation of aimage showing the relative position of the body elements.

It is a further object of this invention to provide a system and methodfor medical or surgical procedures which allows reshaping of the bodyelement(s) during the procedure and still permits the generation of aimage showing the position and current shape of the body elements.

It is a further object of this invention to provide a system which canlocalize a body element and provide a display during the procedure ofthe position of the body element relative to an instrument, such as aforceps, microscope, or laser, so that the instrument can be preciselylocated relative to the body element.

Other objects and features will be in part apparent and in part pointedout hereinafter.

The invention comprises a system for use during a medical or surgicalprocedure on a patient's body. The system generates one or more imagesrepresenting the position and shape of one or more body elements duringthe procedure using scans generated by a scanner prior to the procedure,the scans having at least one reference point for each of the bodyelements of interest. These two dimensional scans, taken together,comprise a three dimensional depiction of the body, and are called theimage data set. The reference points of a particular body element have aspatial relation to the particular body element. The system includesmeans for identifying, during the surgical or medical procedure, theposition of the reference points of each of the body elements to bedisplayed by the system. The system also includes a means processor formodifying the image data set according to the identified position of thereference points of each of the body elements during the medical orsurgical procedure, called the identifying means. The processorgenerates images using a modified (displaced and/or deformed) image dataset representing the position and shape of the body elements during theprocedure. Optionally, the processor determines the position of amedical or surgical instrument relative to these body elements. Thesystem also includes a display which utilizes the modified image dataset generated by the processor to illustrate the position and shape ofthe body elements during the procedure and optionally the determinedposition of the medical or surgical instrument relative to the bodyelements by means of two dimensional images.

The invention also comprises a method for use during a procedure. Themethod generates images representing the position and shape of one ormore body elements during the procedure based on scans generated priorto the procedure, which scan set has reference points for each of thebody elements. The method comprises the steps of:

identifying, during the procedure, the position of the reference pointsof each of the body elements to be displayed;

modifying the image data set according to the identified position of thereference points of each body element during the procedure in order togenerate a modified (displaced and/or deformed) image data setrepresenting the position of the body elements during the procedure;

optionally determining the position of a medical or surgical instrument,probe or beam of irradiation relative to the body elements; and

generating a display based on the modified image data set illustratingthe position and shape of the body elements during the procedure andoptionally the position of the medical or surgical instrument relativeto the body elements.

The invention also comprises a method for use with two or more bodyelements each of which have reference points. Prior to the procedure,the method comprises the steps of placing the body elements in a frameto fix their relative position; and scanning the fixed body elements.During the procedure, the method comprises the steps of:

placing the body elements in the frame so that the body elements havethe same relative position as their position during scanning;

determining the position of reference points on the body elementsrelative to reference means;

determining the position of a medical or surgical instrument relative tothe reference means;

determining the position of the medical or surgical instrument relativeto the body elements; and

generating a display based on the pre-procedural scanning illustratingthe determined position of the medical or surgical instrument relativeto the body elements.

The invention also comprises a device for use with a surgical navigationsystem having a sensor array which is in communication with the deviceto identify its position, the device for use in guiding a catheter, thedevice for engaging a cable connected to the surgical navigation system,the cable for providing signals for activating the device. A handle hasa cavity therein. A plurality of light emitting diodes on the handleemit light, when activated, for communicating with the sensor array ofthe surgical navigation system. A connector attached to the handle andadapted to engage the cable connected to the surgical navigation systemreceives the signals for activating the diodes. Wires located in thecavity of the handle and electrically interconnecting the connector andthe light emitting diodes transmit the signals received by the connectorto the diodes. A guide member connected to the handle guides thecatheter.

The invention also comprises a device for use with a surgical navigationsystem having a sensor array which is in communication with the deviceto identify its position. A base member has a cavity therein. Aplurality of light emitting diodes on the base member emit light, whenactivated, for communicating with the sensor array of the surgicalnavigation system. An activating circuit connected to the diodesprovides signals for activating the diodes. Wires located in the cavityof the base member and electrically interconnecting the power supply andthe light emitting diodes transmit the signals for activating thediodes.

The invention also comprises a device for use with a surgical navigationsystem having a sensor array which is in communication with the deviceto identify its position, the device for engaging a structure attachedto or an instrument in known relation to a body part thereby providing aknown reference relative to the body part, the device having a connectorfor engaging a cable connected to the surgical navigation system, thecable for providing signals for activating the device. A base member hasa cavity therein. A coupling on the base member engages the structure inorder to maintain the base member in fixed relation to the body partthereby providing the fixed reference. A plurality of light emittingdiodes on the base member, said diodes, when activated, emitting lightfor communicating with the sensor array of the surgical navigationsystem. A connector attached to the base member and adapted to engagethe cable connected to the surgical navigation system receives thesignals for activating the diodes. Wires located in the cavity of thebase member and electrically interconnecting the connector and the lightemitting diodes transmit the signals received by the connector to thediodes to activate the diodes.

The invention also comprises a device for use with a surgical navigationsystem having a sensor array which is in communication with the deviceto identify its position, the device for guiding an instrument forengaging a body part thereby locating the instrument at a known positionrelative to the body part, the device having a connector for engaging acable connected to the surgical navigation system, the cable forproviding signals for activating the device. A housing has a cavitytherein. A structure on the housing guides the instrument in order tomaintain the instrument in a relationship relative to the housing. Aplurality of light emitting diodes on the housing, when activated, emitlight for communicating with the sensor array of the surgical navigationsystem. A connector attached to the housing and adapted to engage thecable connected to the surgical navigation system receives the signalsfor activating the diodes. Wires located in the cavity of the housingand electrically interconnecting the connector and the light emittingdiodes and for transmitting the signals received by the connector to thediodes to activate the diodes.

In addition, the invention comprises a surgical navigation systemcomprising:

a controller;

a sensor array;

a reference frame in communication with the array to identify itsposition; and

a localization frame in communication with the array to identify aposition of the localization frame, the localization frame for guidingthe instrument for engaging the body part thereby locating theinstrument at a known position relative to the body part, thelocalization frame connected to the controller which provides signalsfor activating the localization frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the prior art system in which rigidfixation and absence of movement between imaging and surgery permits aone-to-one registration process between the pre-surgical scan and theposition in surgery.

FIG. 2A is an illustration of operation of the invention in which thepre-procedural image data set is modified in accordance with theintra-procedural position in order to generate a displaced and/ordeformed data set representative of the intra-procedural position.

FIG. 2B is a block diagram of one preferred embodiment of a systemaccording to the invention.

FIG. 3 is an illustration of the pre-procedural alignment of three bodyelements during scanning.

FIG. 4 is an illustration of the intra-procedural alignment of the threebody elements of FIG. 3 during surgery.

FIG. 5 is an illustration of three body elements, one of which has areference frame attached thereto, in combination with a registrationprobe.

FIG. 6 is an illustration showing ultrasound registration according tothe invention in which emitters are attached to the ultrasound for avirtual reference and, optionally, the patient's body for an actualreference.

FIG. 7 is an illustration of a fluoroscopic localizer according to theinvention for providing projections of an image of the body elements.

FIG. 8 is an illustration of a drill guide instrument of the inventionwherein the position of a drill guide relative to the body elements maybe displayed.

FIGS. 9 and 10 illustrate a clamped reference frame and a wiredreference frame, respectively.

FIG. 11 is a schematic diagram of one preferred embodiment of a cranialsurgical navigation system according to the invention.

FIG. 11A is a top plan view of one preferred embodiment of a cranialreference arc frame according to the invention.

FIG. 11B is a side plan view, partially in cross section, of onepreferred embodiment of a cranial reference arc frame according to theinvention.

FIG. 11C is a wiring diagram of one preferred embodiment of a cranialreference arc frame according to the invention.

FIG. 12A is a top plan view of one preferred embodiment of a spinalreference arc frame according to the invention.

FIG. 12B is a front plan view, partially in cross section, of onepreferred embodiment of a spinal reference arc frame according to theinvention.

FIG. 12C is a side plan view of one preferred embodiment of a spinalreference arc frame according to the invention.

FIG. 12D is a top plan view of one preferred embodiment of athoraco-lumbar mount according to the invention.

FIG. 12E is a front plan view, partially in cross section, of onepreferred embodiment of a thoraco-lumbar mount according to theinvention.

FIG. 12F is a side plan view of one preferred embodiment of athoraco-lumbar mount according to the invention.

FIG. 12G is a wiring diagram of one preferred embodiment of a spinalreference arc frame according to the invention.

FIG. 13A is a top plan view of one preferred embodiment of a biopsyguide localization frame according to the invention.

FIG. 13B is a side plan view, partially in cross section, of onepreferred embodiment of a biopsy guide localization frame according tothe invention.

FIG. 13C is a front plan view of one preferred embodiment of a biopsyguide localization frame according to the invention.

FIG. 13D is a top plan view of one preferred embodiment of a drill guidelocalization frame according to the invention.

FIG. 13E is a side plan view, partially in cross section, of onepreferred embodiment of a drill guide localization frame according tothe invention.

FIG. 13F is a top plan view of one preferred embodiment of a drill yokelocalization frame according to the invention.

FIG. 13G is a side plan view, partially in cross section, of onepreferred embodiment of a drill yoke localization frame according to theinvention.

FIG. 13H is a top plan view of one preferred embodiment of aventriculostomy probe including an integrated localization frameaccording to the invention.

FIG. 13I is a side plan view, partially in cross section, of onepreferred embodiment of a ventriculostomy probe including an integrallocalization frame according to the invention.

FIG. 13J is a wiring diagram of one preferred embodiment of alocalization frame according to the invention.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 2A and 2B, an overview of operation of one preferredembodiment of the system according to the invention is illustrated.Prior to a particular procedure, the body elements which will be part ofthe procedure are scanned to determine their alignment, i.e., theirpre-operative position. For example, the alignment may be such asillustrated in FIG. 3 wherein body elements 10, 20, and 30 are more orless aligned in parallel. These body elements may be bones or otherrigid bodies. In FIG. 3, three-dimensional skeletal elements 10, 20, 30are depicted in two dimensions as highly stylized vertebral bodies, withsquare vertebra 11, 21, 31, small rectangular pedicles 12, 22, 32, andtriangular spinous processes 13, 23, 33. During imaging, scans are takenat intervals through the body parts 10, 20, 30 as represented in FIG. 3by nine straight lines generally referred to be reference character 40.At least one scan must be obtained through each of the body elements andthe scans taken together constitute a three-dimensional pre-proceduralimage data set.

FIG. 2B is a block diagram of the system according to the invention. Ascanner interface 102 allows a processor 104 to obtain thepre-procedural image data set generated by the scanner and store thedata set in pre-procedural image data set memory 106. Preferably, afterimaging, processor 104 applies a discrimination process to thepre-procedural image data set so that only the body elements 10, 20, 30remain in memory 106. If a discrimination process is employed, processor104 may execute the discrimination process while data is beingtransferred from the scanner through the scanner interface 102 forstorage in memory 106. Alternatively, memory 106 may be used for storingundiscriminated data and a separate memory (not shown) may be providedfor storing the discriminated data. In this alternative, processor 104would transfer the data set from the scanner through scanner interface102 into memory 106 and then would discriminate the data stored inmemory 106 to generate a discriminated image data set which would bestored in the separate memory.

Once the body elements 10, 20, 30 are discriminated and each defined asa single rigid body, they can be repositioned by established softwarealgorithms to form the displaced image data set. Each rigid bodyelement, 10, 20, 30, must have at least three recognizable referencepoints which are visible on the pre-procedural images. These referencepoints must be accurately detected during the procedure. For body part10, reference points 10A, 10B, and 10C are located on the spinousprocess 13; for body part 20, reference points 20A and 20C are locatedon the vertebra 21 and reference point 20B is located on spinous process23; and for body part 30, reference points 30A and 30B are located onthe spinous process 33 and reference point 30C is located on thevertebra 31. More than one reference point can be selected on each scanthrough the bone, although the maximal accuracy of registration isachieved by separating the reference points as far as possible. Forexample, in the case of posterior spinal surgery, it may be preferableto select reference points 10A, 10B, and 10C on the spinous processwhich is routinely exposed during such surgery. It is contemplated thatsystem software may allow the manual or automated identification ofthese same points on the images of the body elements 10, 20, 30. As FIG.3 is a two-dimensional projection of a three-dimension process, thereference points will not be limited to a perfect sagittal plane, asdepicted.

After imaging, the skeletal body elements 10, 20, 30 may move withrespect to each other at the joints or fracture lines. In the procedureroom, such as an operating room or a room where a medical procedure willbe performed, after positioning the patient for surgery, the bodyelements will assume a different geometry, such as the geometry depictedin FIG. 4.

As a result of this movement, the preprocedural image data set stored inmemory 106, consisting of the scans through the skeletal elements, doesnot depict the operative position of the skeletal elements, as shown inFIG. 4. However, the shape of the skeletal elements, as depicted by thescans through the element, is consistent between imaging and proceduresince they are rigid bodies, as indicated by the lines 40 through eachelement in FIG. 4. Therefore, the image data set must be modified todepict the intraprocedural geometry of the skeletal elements. Thismodification is performed by identifying the location of each referencepoint of each skeletal element in procedure space. As diagrammaticallyillustrated in FIGS. 2A and 2B, a localizer 108 (see FIG. 13, below, formore details) identifies the location and provides this information sothat the pre-procedural data set may be deformed or re-positioned intothe displaced data set. As a result, the displaced data set is inregistration with the intra-procedural position of the elements 10, 20,30. Once the locations of the reference points are determined by thelocalizer 108, processor 104, which is a part of the work station, canexecute software which re-positions the images of the skeletal elementsto reflect the position of the actual elements in the procedure roomthus forming the displaced set and the registration between thedisplaced set and the intra-procedural position.

Preferably, a three-dimensional digitizer may be used as the localizer108 to determine the position and space of the elements 10, 20, 30during the procedure. In general, the digitizer would include areference array 110 which receives emissions from a series of emitters.Usually, the emissions consist of some sort of energy, such as light,sound or electromagnetic radiation. The reference array 110 is distantfrom the emitters which are applied to and positioned in coordinationwith the elements being localized, determining the position of theemitters. As is apparent, the emitters may be placed distant to theelements and the reference array 110 may be attached to the elementsbeing localized.

Referring to FIGS. 2A and 2B, an alternate preferred embodiment of thesystem according to the invention in the case where the body elementsare not rigid, but rather semi-rigid such that shape deformations mayoccur to the body elements is described as follows. Prior to aparticular procedure, the body elements which will be part of theprocedure are scanned to determine their pre-operative position andshape. For example, the alignment may be such as illustrated in FIG. 3wherein body elements 10, 20, and 30 are more or less aligned inparallel and have a defined shape. These body elements may be softtissue such as the prostate or other semirigid bodies.

After imaging, the elements 10, 20, 30 may move with respect to eachother and also their shape may become deformed. In the procedure room,such as an operating room or a room where a medical procedure will beperformed, after positioning the patient for surgery, the body elementsmay assume a different geometry, such as the geometry depicted in FIG. 4where geometry depicts both element alignment (position) and shape.

As a result of this changed geometry, the pre-procedural image data setstared in memory 106, does not depict the operative geometry of the bodyelements, as shown in FIG. 4. Indeed, the shape of the body elements, asdepicted by the scan through the element, may have changed betweenimaging and procedure since they are semi-rigid bodies. Therefore, theimage data set must be modified to depict the current geometry of thebody elements. This modification is performed by identifying thelocation of the reference points of each body element in procedurespace. As diagrammatically illustrated in FIG. 2B, a localizer 108,possibly in communication with a processor 104, identifies the locationof the reference points and provides this information so that thepreprocedural data set may be deformed into the displaced data set. Oncethe locations of the reference points are determined, processor 104,which is a part of the work station, can execute software which modifiesthe images of the body elements to reflect the geometry of the actualelements in the procedure room thus forming the displaced set and theregistration between the displaced set and the intra-proceduralposition. As a result, the, displaced data set is in registration withthe intra-procedural geometry of the elements 10, 20, 30.

According to one preferred embodiment of the invention, a referenceframe 116 is attached to one of the body elements 10 at the beginning ofthe procedure. Various reference frame embodiments are illustrated inmore detail in FIGS. 11 and 11A–11C and 12A–12G, below. Reference frame116 is equipped with a plurality of emitters 114 which together define athree-dimensional intraprocedural coordinate system with respect to thebody element 10. In conventional terms, the reference frame 116 definesthe stereotactic space with respect to the body element 10. Emitters 114communicate with sensors 112 on a reference array 110 located in thepracerinre room and remote from the reference frame 116 and patient. Ifthe body of the patient is not immobilized during surgery, then multiplereference frames may be required for each body element to define asurgical space with respect to each element. The surgical space mayalternatively be defined by rigid fixation of the frame emitters 114directly (or indirectly, for example, to the skin) to the skeletalelements 10, 20, or 30. In either case, the emitters 114 emit a signalwhich is received by the sensors 112. The received signal is digitizedto compute position, for example, by triangulation. Through suchinformation, the localizer 108 or a digitizer which is part of thelocalizer 108 can determine the exact three-dimensional position of theframe emitters 114 relative to the sensors 112. Thereby, localizer 108or the processor 104 can exactly determine the position of the referenceframe 116 relative to the array which is free to move except duringlocalization, e.g., activation of the emitters 114 on the referenceframe 116 and activation of the probe emitters 112. Emitters 114 of thereference frame 116 are energized to provide radiation to the sensors112, which radiation is received and generates signals provided to thelocalizer 108 for determining the position of the frame 116 relative tothe array 110.

Next, it is necessary to determine the position of the body element 10,which may be a skeletal element, to which the reference frame 116 isaffixed or positioned with respect to. In particular, the position ofthe body element 10 relative to the reference frame 116 must bedetermined, thereby determining the position of the body element 10 inthe surgical space defined by the reference frame 116. After exposure ofthe reference points 10A, 10B, 10C by surgical dissection, the referencepoints are touched by the tip of a registration probe lie equipped withemitters 3–20. As each of the reference points 10A, 10B, 10C is touchedby the tip of the probe 120, the emitters are energized to communicatewith the sensors 112 of reference array 110. This communication permitsthe localizer 108 to determine the position of the registration probe120, thereby determining the position of the tip of the probe 120,thereby determining the position of the reference point 10A on which thetip is positioned. By touching each of the reference points 10A, 10B,10C on each body element 10, 20, 30 involved in the procedure, anintra-procedural geometry data is generated and stored in memory 121.This data is related to the corresponding reference points on thepre-procedural images of the same elements by processor 104 whichemploys software to derive a transformation which allows thedetermination of the exact procedural position, orientation, and shapein surgical space of each body element, and thereby modifies thepreprocedural image data set stored in memory 106 to produce a displacedimage data set which is stored in memory 123. The displaced image dataset in memory 123 reflects the geometry of the actual elements 10, 20,30 during the procedure. Processor 104 displays the displaced image dataset on display 125 to provide a visual depiction of the geometry of thebody elements 10, 20,30 during the procedure. This image is used duringthe procedure to assist in the procedure. In addition, it iscontemplated that an instrument, such as a forceps, a laser, amicroscope, an endoscope, or a radiation delivery system, which would beused during the procedure, may be modified by the addition of emitters.This modified device when moved into the area of the body elements 10,20, 30 would be activated so that its emitters would communicate withthe reference array 110 thereby permitting localizer 108 to determinethe instrument's position. As a result, processor 104 would modifydisplay 124 to indicate the position of the instrument, or theinstruments focal point, such as by positioning a cursor, with respectto the body elements 10, 20, 30.

Further, it is contemplated that the addition of emitters on aninstrument (effector) may be used with the system in order to create aclosed-loop feedback for actively (in the case of robotics) or passivelycontrolling or monitoring the instrument and its position. Such acontrol loop allows the monitoring of certain procedures such as thedelivery of radiation to the body or the use of a drill where the objectof the procedure is to keep the focal point of the instrument in a safezone, i.e. a predetermined procedural plan. Such a control loop couldalso control the operation of a robotically controlled instrument wherethe robotics could be driven (directly or indirectly) by processor 104to control the position the position of the instrument. For example, theprocessor could instruct a robotic arm to control the position of alaser. The laser position could be monitored, such as by emitters on thelaser. The processor would be programmed with the control parameters forthe laser so that it would precisely follow a predetermined path.

Reference frame 116 allows the patient to be moved during the procedurewithout the need for re-registering the position of each of the bodyelements 10, 20, 30. It is assumed that during the procedure, the bodyelements are fixed relative to each other. Since the reference frame 116is fixed (directly or indirectly) to body element 10, movement of thepatient results in corresponding movement of the reference frame 116.Periodically, or after each movement of the patient, frame emitters 114may be energized to communicate with the sensors 112 of reference array110 in order to permit localizer 108 to determine the position of thereference frame 116. Since the reference frame 116 is in a knownrelative position to element 110 and since we have assumed that elements20 and 30 are in fixed relation to element 10, localizer 108 and/orprocessor 104 can determine the position of the elements and therebymaintain registration.

An alternative to touching the reference points A, B, C with the tip ofthe probe 118 would be to use a contour scanner 126 a with emittersattached 126 b. Such a device, using some form of energy such as soundor light which is emitted, reflected by the contour and sensed, wouldallow the extraction of a contour of the body elements 10, 20, 30, thusserving as a multitude of reference points which would allowregistration to occur. The registration process is analogous to theprocess described for ultrasound extracted contours below.

In certain situations, markers may be used on the skin surface asreference points to allow the transformation of the pre-procedural imagedata set into the displaced image data set. Reciprocally, skin surfacefiducials applied at the time of imaging can be used to re-position thebody to match the geometry during imaging and is described below.

Localization of body elements 10, 20, 30 may be desired withoutintra-procedural exposure of the reference points A, B, C on those bodyelements. Examples wherein the spine is minimally exposed includepercutaneous biopsy of the spine or discectomy, spinal fixation,endoscopy, percutaneous spinal implant insertion, percutaneous fusion,insertion of drug delivery systems, and radiation delivery. In thissituation, localization of reference points on the body elements must bedetermined by some form of imaging which can localize through overlyingsoft tissue and/or discriminate surrounding tissue and structures. Thereare currently two imaging techniques which are available to a surgeon inthe operating room or a doctor in a procedure room which satisfy theneeds of being low cost and portable. Both imaging techniques,ultrasonography and radiography, can produce two- or three-dimensionalimages which can be employed in the fashion described herein to registera three-dimensional form such as a skeletal element.

As described in U.S. patent application Ser. Nos. 07/858,980 and08/053,076, the entire disclosures of which are incorporated herein byreference, the coupling of a three-dimensional digitizer to a probe ofan ultrasound device affords benefits in that a contour can be obtainedwhich can be related directly to a reference system that definesthree-dimensional coordinates in the procedural work space, i.e., thesurgical space. In the context of the present invention, a patient isimaged prior to a procedure to generate a pre-procedural image data setwhich is stored in memory 106. In the procedure room, the patient's bodyis immobilized to stabilize the spatial relationship between the bodyelements 10, 20, 30. A procedural reference system, surgical space, forthe body is established by attaching a reference frame 116 to one of thebody elements or by otherwise attaching emitters to the patient or bodyelements as noted above, or by attaching emitters to a device capable oftracking one of the body elements thereby forming a known relationshipwith the body element. For example, this could be performed by using thepercutaneous placement of a reference frame similar to the one describedabove, radiopaque markers screwed into the elements or by placingemitters 130 directly on the skins, as illustrated in FIG. 6, based onthe assumption that the skin does not move appreciably during theprocedure or in respect to the body elements.

An ultrasound probe 128 equipped with at least three emitters 130 isthen placed over the body element of interest. The contour (which ran beeither two- or three-dimensional) of the body element is then obtainedusing the ultra-sound probe 128. This contour can be expressed directlyor indirectly in the procedural coordinates defined by the referencesystem (surgical space). Emitters 130 communicate with sensors 112 ofreference array 110 to indicate the position of the ultrasound probe128. An ultrasound scanner 166 which energizes probe 128 to determinethe contour of the body element of interest being scanned. This contourinformation is provided to processor 104 for storage in intra-proceduralgeometry data memory 121.

The intra-procedural contour stored in memory 121 is then compared by acontour matching algorithm to a corresponding contour extracted from thepre-operative image data set stored in memory 106. Alternatively, apre-procedural contour data set may be stored in memory 134 based on apre-procedural ultrasound scan which is input into memory 134 viascanner interface 102 prior to the procedure. This comparison processcontinues until a match is found for each one of the elements. Throughthis contour matching process, a registration is obtained between theimages of each body element and the corresponding position of eachelement in the procedural space, thereby allowing the formation of thedisplaced image data set 123 used for localization and display. Notethat the contours used in the matching process only have to besufficiently identical to accomplish a precise match—the contours do nothave to be the same extent of the body element.

In certain instances, the ultrasound registration noted above may not beapplicable. For example, ultrasound does not penetrate bone, and thepresence of overlying bone would preclude the registration of anunderlying skeletal element. Further, the resolution of ultrasounddeclines as the depth of the tissue being imaged increases and may notbe useful when the skeletal element is so deep as to preclude obtainingan accurate ultrasonically generated contour. In these circumstances, aradiological method is indicated, which utilizes the greater penetratingpower of x-rays.

Pre-operative imaging occurs as usual and the skeletal elements may bediscriminated from the soft tissue in the image data set as above. Inparticular, a CT scan of the skeletal elements 10, 20, 30 could be takenprior to the procedure. Processor 104 may then discriminate the skeletalelements and store the pre-procedural image data set in memory 106.Next, the patient is immobilized for the procedure. A radiograph of theskeletal anatomy of interest is taken by a radiographic device equippedwith emitters detectible by the digitizer. For example, a fluoroscopiclocalizer 136 is illustrated in FIG. 7. Localizer 136 includes a devicewhich emits x-rays such as tube 138 and a screen 140 which is sensitiveto x-rays, producing an image when x-rays pass through it. This screenis referred to as a fluoroscopic plate. Emitters 142 may be positionedon the tube 138, or on the fluoroscopic plate 140 or on both. Fordevices in which the tube 138 is rigidly attached to the plate 140,emitters need only be provided on either the tube or the plate.Alternatively, the reference array 110 may be attached to the tube orthe plate, obviating the need for emitters on this element. By passingx-rays through the skeletal element 141 of interest, a two-dimensionalimage based on bone density is produced and recorded by the plate. Theimage produced by the fluoroscopic localizer 136 is determined by theangle of the tube 138 with respect to the plate 140 and the position ofthe skeletal elements therebetween and can be defined with respect toprocedure coordinates (surgical space). Fluoroscopic localizer 136includes a processor which digitizes the image on the plate 140 andprovides the digitized image to processor 104 for possible procesing andsubsequent storage in intra-procedural geometry data memory 121.Processor 104 may simulate the generation of this two-dimensional x-rayimage by creating a series of two-dimensional projection of thethree-dimensional skeletal elements that have been discriminated in theimage data set stored in memory 106. Each two dimensional projectionwould represent the passage of an X-ray beam through the body at aspecific angle and distance. In order to form the displaced data set andthus achieve registration, an iterative process is used which selectsthat a two-dimensional projection through the displaced data set thatmost closely matches the actual radiographic image(s) stored in memory121. The described process can utilize more than one radiographic image.Since the processor 104 is also aware of the position of thefluoroscopic localizers because of the emitters 142 thereon, which arein communication with localizer 108, the exact position of the skeletalelements during the procedure is determined.

As noted above, the procedural reference system or surgical space forthe body can be established by attaching emitters to a device capable ofdetecting and tracking, i.e. identifying, one of the body elementsthereby forming a known relationship with the body element. For example,the emitters 130 on the ultrasound probe 128 together and without thethree emitters on the patient's body form a type of reference frame 116as depicted in FIG. 6 which can be virtually attached to body element 10by continuously or periodically updating the ultrasound contour of bodyelement 10 stored in intra-procedural geometry data memory 121 which theprocessor 104 then uses to match to the contour of body element 10stored in pre-procedural memory 106 thereby continuously or periodicallyupdating the displaced image data set in memory 122 so that registrationwith the procedural position of the body elements is maintained. It iscontemplated that a virtual reference frame can be accomplished usingany number of devices that are capable of detecting and tracking a bodyelement such as radiographic devices (fluoroscope), endoscopes, orcontour scanners.

The above solutions achieve registration by the formation of a displacedimage data set stored in memory 123 which matches the displacement ofthe skeletal elements at the time of the procedure. An alternativetechnique to achieve registration is to ensure that the positions of theskeletal elements during the procedure are identical to that found atthe time of imaging. This can be achieved by using a frame that adjustsand immobilizes the patient's position. In this technique, at leastthree markers are placed on the skin prior to imaging. These markershave to be detectible by the imaging technique employed and are calledfiducials. A multiplicity of fiducials is desirable for improvingaccuracy.

During the procedure, the patient's body is placed on a frame thatallows precise positioning. Such frames are commonly used for spinalsurgery and could be modified to allow their use during imaging andcould be used for repositioning the patient during the procedure. Theseframes could be equipped with drive mechanisms that allow the body to bemoved slowly through a variety of positions. The fiducials placed at thetime of imaging are replaced by emitters. By activating the drivemechanism on the frame, the exact position of the emitters can bedetermined during the procedure and compared to the position of thefiducials on the pre-procedural image data set stored in memory 106.Once the emitters assume a geometry identical to the geometry of thefiducials of the image data set, it is considered that the skeletalelements will have resumed a geometric relationship identical to theposition during the pre-procedural scan, and the procedure can beperformed using the unaltered image data set stored in memory 106.

In general, instrumentation employed during procedures on the skeletonis somewhat different than that used for cranial applications. Ratherthan being concerned with the current location, surgery on the skeletonusually consists of placing hardware through bones, taking a biopsythrough the bone, or removing fragments. Therefore, the instrumentationhas to be specialized for this application.

One instrument that is used commonly is a drill. By placing emitters ona surgical drill, and by having a fixed relationship between the drillbody and its tip (usually a drill bit), the direction and position ofthe drill bit can be determined. At least three emitters would be neededon the drill, as most drills have a complex three-dimensional shape.Alternatively, emitters could be placed on a drill guide tube 800 havingemitters 802, and the direction 804 of the screw being placed or holebeing made could be determined by the digitizer and indicated on theimage data set (see FIG. 8). The skeletal element 806 would also haveemitters thereon to indicate its position.

Besides modification of existing instrumentation, new instrumentation isrequired to provide a reference system for surgery as discussed above.These reference frames, each equipped with at least 3 emitters, requirefixation to the bone which prevents movement or rotation.

For open surgery, a clamp like arrangement, as depicted in FIG. 9, canbe used. A clamp 900 is equipped with at least two points 902, 904, 906,908 which provide fixation to a projection 910 of a skeletal element. Byusing at least two point fixation the clamp 900, which functions as areference frame, will not rotate with respect to the skeletal element.The clamp includes emitters 912, 914, 916 which communicate with thearray to indicate the position of the skeletal element as it is movedduring the procedure.

Many procedures deal with bone fragments 940 which are not exposedduring surgery, but simply fixated with either wires or screws 950, 952introduced through the skin 954. FIG. 10 depicts a reference platform956 attached to such wires or screws 950, 952 projecting through theskin 954. The platform 956 includes a plurality of emitters 958, 960,962, 964 which communicate with the array to indicate the position ofthe bone fragment 940 as it is moved during the procedure.

The reference frame can be slipped over or attached to the projectingscrews or wires to establish a reference system. Alternatively, theframe can be attached to only one wire, as long as the method ofattachment of the frame to the screw or wire prevents rotation, and thatthe wire or screw cannot rotate within the attached skeletal element.

Reference and Localization Frames

FIG. 11 is a schematic diagram of one preferred embodiment of a cranialsurgical navigation system according to the invention. Portable systemcabinet 102 includes a surgical work station 104 which is supported forviewing by the surgeon or technician using the system. Work station 104includes a screen 106 for illustrating the various scans and isconnected to a personal computer 108 for controlling the monitor 106.The system also includes an optical digitizer including a camera array110, a camera mounting stand 112 for supporting the array remote fromand in line of sight with the patient, a digitizer control unit 114 onthe portable system cabinet 102 and connected to the computer 108, afoot switch 116 for controlling operation of the system and a breakoutbox 118 for interconnecting the foot switch 116 and the digitizercontrol unit 114.

Also connected via the break out box 118 is a reference frame assembly120 including a reference frame 122 with cable connected to the breakout box 118, a vertical support assembly 124, a head clamp attachment126 and a horizontal support assembly 129. Optical probe 164 (which is alocalization frame) is also connected via cable to the digitizer controlunit 114 via the break out box 118.

In operation, a patient's head (or other “rigid” body element) isaffixed to the head clamp attachment 127. To determine the position ofoptical probe 164 with respect to the head within the head clampattachment 127, a surgeon would step on pedal 116 to energize theemitters of reference frame 122. The emitters would generate a lightsignal which would be picked up by camera array 110 and triangulated todetermine the position of the head. The emitters of the optical probe130 would also be energized to emit light signals which are picked up bythe camera array to determine the position of the optical probe 164.Based on the relative position of the head and the probe 164, controlbox 114 would illustrate a preoperative scan on the screen of monitor106 which would indicate the position of the probe relative to and/orwithin the head.

FIG. 11A is a top plan view of one preferred embodiment of a cranialreference arc frame 122 according to the invention. Reference frame 122is for use with a surgical navigation system such as illustrated in FIG.11 having a sensor array such as camera array 110 which is incommunication with the reference frame 122 to identify its position. Thereference frame 122 includes a base member 132 having an upper base 134and a base plate 136 which each have a semi-circular configuration andare joined together by screws 138 to form a cavity 140 therebetween. Thebase and plate may be made of anodized aluminum or other autoclavablematerial. The top of the upper base may be provided with one or morespring clamps 142 for engaging a Leyla retractor arm. As shown in FIG.11A, the upper base is provided with five spring clamps 142.

Either or both ends of the reference frame 122 may be provided with abayonet fitting 144 for engaging a clamp which would also engage a Leylaretractor. One or both ends of the reference frame 122 is also formedinto a radial projection 146 for supporting a screw 148 and crank handle150 used to lock the reference frame to a head clamp such as head clamp127 shown in FIG. 11 or a Mayfield clamp. This allows the referenceframe 122 to be placed in a fixed position relative to the head so thatany movement of the head would also include corresponding movement ofthe reference frame 122.

Radial projection 146, screw 148 and handle 150 constitute a coupling onthe base member 132 for engaging a structure attached to a body part(the head) thereby providing a fixed reference relative to the head inorder to maintain the base member 132 in fixed relation to the head.

Equally spaced about the reference frame 122 are a plurality of LEDs 152for communicating with the camera array 110. The LEDs 152 are mounted inholes 154 in the upper base 134, which holes 154 are in communicationwith the cavity 140. Wires 156 are connected to each of the terminals ofthe LEDs 152 are positioned within the cavity 140. The other ends of thewires are connected to a connector 158 for engaging a cable connected tothe digitizer 114 of the surgical navigation system. The cable providessignals for activating the LEDs 152. Connector 158 is mounted on asupport projection 160 which projects from the base plate 136. Thissupport projection 160 has a channel therein for permitting the wires tobe connected to the connector 128. FIG. 11C is a wiring diagram of onepreferred embodiment of the reference frame 122 according to theinvention. As is illustrated in FIG. 11C, each LED terminal is connectedto a separate pin of the connector 158. Although the invention isillustrated as having a connector for engaging a cable, it iscontemplated that the reference frame 122 may be battery operated sothat no cable is necessary.

The reference frame 122 is essentially a semi-circular arc so that itfits around the head of the patient to allow communication of multipleLEDs 152 on the reference frame 122 with the camera array 110. Themultiple LEDs 152 on the reference frame 122 are positioned in aprecisely known geometric arrangement so that the calibration of thecamera array 110 can be checked continuously by comparing the LEDsgeometric positions as calculated by the digitizer 114 with thoseprecisely known geometric positions. Inconsistencies in this informationindicates the need to recalibrate the system or to reposition thereference frame 122 so that it can more accurately communicate with thecamera array 110. Frame 122 also includes a calibration divot 162. Inparticular, divot 162 is an exactly located depression within the upperbase 134 and is used to calibrate or check the calibration during themedical or surgical procedure the position of the tip of the probe. Theprecise location of each of the LEDs 152 relative to the calibrationdivot 162 is known. Therefore, locating a tip of a localization frameprobe in the calibration divot 162 allows the calibration or thecalibration check of the probes in the following manner. The tip of theprobe is located within the calibration divot 162 and the LEDs on theprobe are energized to provide light signals to the camera array 110.The LEDs on the reference frame 122 are also energized to communicatewith the camera array 110. Using the known position of the divot 162with respect to the position of each of the LEDs 152 as calculated bythe digitizer 114, the location of the calibration divot 162 is comparedto the location of the tip of the probe as calculated by the digitizerusing the LEDs on the probe in order to confirm that there is nodistortion in the probe tip relative to the divot 162. Distortion in theprobe tip indicates the need to recalibrate the probe so that it canmore accurately communicate with the camera array 110 or to retire theprobe.

FIGS. 12A, 12B, and 12C illustrate another preferred embodiment of thereference frame in the form of a spine reference arc frame 200. As withreference frame 122, spine reference arc frame 200 has an upper base 202which engages a base plate 204 to form a cavity 206 therebetween. Asshown in FIG. 12A, the spine reference arc frame 200 has a generallyU-shape configuration with LEDs 208 located at the ends of the legs 209of the U-shaped member and at the intersection of the legs and base 211of the U-shaped member. Projecting laterally from the base 211 is acoupling 210 for engaging a thoraco-lumbar mount 212 as illustrated inFIGS. 12D, 12E, and 12F. Also positioned on the base 211 is acalibration divot 214 which is a depression having the same purpose asthe calibration divot 162 of the reference frame 122. Coupling 210 hastwenty-four evenly spaced teeth 216 arranged in a circular pattern forengaging the twenty-four equally spaced teeth 218 of the thoraco-lumbarmount. This allows the spine reference arc frame 200 to be positioned toform various angles relative to the mount 212. It is contemplated thatany other variable position connector may be used to join the spinereference arc frame 200 and the mount 212. Base plate 204 has an openingtherein for engaging a connector 220 for receiving a cable to thedigitizer control unit 114. The LEDs 208 are connected to the connector220 by wires 222 as illustrated in wiring diagram FIG. 12G.

Referring to FIGS. 12D, 12E, and 12F, thoraco-lumbar mount 212 comprisesa clamp shaft 224 having an axial bore therein within which ispositioned an actuating shaft 226 which is connected to an actuatingknob 228 extending beyond the end of clamp shaft 224. The end of theactuating shaft 226 opposite the actuating knob 228 has an internalthreaded bore 230 which engages external threads of an actuation screw232. A U-shaped head 234 of screw 232 supports a pivot pin 236 betweenits legs. The pivot pin passes through the jaws 238 so that the jaws 238rotate about the pivot pin 236 and move relative to each other defininga receiving area 240 within which a spinal bone or other body part maybe clamped. The jaws 238 have teeth 239 for engaging a spinal bone orother body part and are spring loaded and held in their open position byspring plungers 242. As the actuating knob 228 is turned to engage thethreads of actuation screw 232, the screw 232 is drawn into the bore 230also drawing the jaws into a housing 246. This results in the cammingsurfaces 244 of housing 246 engaging the follower surfaces 248 of thejaws 238 closing the jaws and closing the receiving area 240 as the jawsare pulled into the housing.

The other end of clamp shaft 224 has a perpendicular projection 250 forsupporting the teeth 218 which engage the teeth 216 of the coupling 210of the spine reference arc frame 200. A spine reference arc clamp screw252 passes through the array of teeth 218 and engages a threaded opening254 in the coupling 210 of frame 200. Screw 252 engages opening 254 andlocks teeth 216 and teeth 218 together to fix the angle between thespine reference arc frame 200 and the thoraco-lumbar mount 212. As aresult, when the mount 212 is connected to a bone by placing the bone inthe receiving area 240 and turning the actuating knob 228 to close thejaws 238 and the receiving area, the frame 200 is in a fixed positionrelative to the bone which is engaged by the jaws. Any movement of thebone results in movement of the frame 200 which can be detected by thecamera array 110.

Referring to FIGS. 13A, 13B and 13C, one preferred embodiment of alocalization biopsy guide frame 300 is illustrated. In general, theframe 300 includes a localization frame 302 which supports a biopsyguide 304 and which also supports a support pin 306. The localizationframe 302 is comprised of an upper base 308 and a base plate 310 whichjoin to form a cavity 312 within which the wires 314 connecting to theLEDs 316 are located. As shown in the FIG. 13A, the localization framehas an elongated portion 318 and a generally V-shaped portion 320 havinglegs 322 and 324. An LED 316 is located at the end of each of the legs322 and an LED 316 is also located at the ends of the elongated portion318. As a result the four LEDs 316 form a rectangular array. However,the underlying localization frame 302 does not have a rectangularconfiguration which allows it to be adapted for other uses, such as adrill guide assembly as illustrated and described below with regard toFIGS. 13D and 13E. In general, the V-shaped portion 320 extendslaterally from the elongated portion 318 in order to accomplish therectangular configuration of the LEDs 316. Note that a rectangularconfiguration for the LEDs 316 is not required and that in fact, atrapezoidal configuration for the LEDs 316 may be preferred in order touniquely distinguish the orientation of the localization frame 302.Support pin 306 passes through the upper base 308 and is essentiallyparallel to a linear axis defined by the elongated portion 318. Thepurpose of support pin 306 is to allow clamps to engage it so that thelocalization biopsy guide frame 300 can be placed in a particularposition relative to a body part in order to guide a biopsy needle.

In order to guide a biopsy needle, the localization frame 302 is fittedwith a biopsy guide 304 which is mounted to the top of the upper base308 and held in place by a clamp 328 which engages the upper base 308via four screws 330. The upper base 308 is also provided with asemicircular channel 332 which forms a seat for receiving the biopsyguide 326. The guide 304 comprises a hollow tube 334 having a collar 336at one end thereof, which has a threaded radial opening for receivingset screw 338.

The base plate 310 is fitted with a connector 340 for engaging a cablewhich is connected to the digitizer 114 for providing signals forenergizing the LEDs 316. FIG. 12G illustrates one preferred embodimentof a wiring diagram which interconnects the connector 340 and four LEDs.

The localization frame 302 is made of the same material as the referenceframe 122, i.e., ULTEM 1000 black which is autoclavable. The biopsyguide 304 may be stainless steel or any other autoclavable metal orplastic material. As with the reference frame, the localization framemay be battery operated thereby avoiding the need for a cable or aconnector for engaging the cable.

FIGS. 13D and 13E illustrate another localization device in the form ofa localization drill guide assembly 350. The assembly 350 includes alocalization frame 302 which is the same as the frame used for thelocalization biopsy guide frame 300, except that it does not have asupport pin 306. It does have a semicircular channel 332 in the upperbase 308 which receives a handle and drill guide assembly 354 instead ofthe biopsy guide tube assembly 304. Assembly 354 includes a handle 356which is used by the surgeon, doctor, technician or nurse conducting theprocedure. Handle 356 has a bore 358 therein for receiving a shaft 360which is seated within the semicircular channel 332. The shaftterminates into an integral collar 362 which supports a drill guide tube364. The axis of the drill guide tube 364 is at an angle relative to theaxis of the shaft 360 to assist in aligning the drill guide tube 364relative to the point at which the drill bit will be entering thepatient's body. In one preferred embodiment, handle and drill guideassembly 354 is a standard off-the-shelf instrument which is mounted tothe channel 332 of the localization frame 302. The handle and drillguide assembly 354 may be a Sofamor Danek Part 870-705. Screws 366(having heads insulated with high temperature RTV compound) attach theshaft 360 to the upper base 308 of the localization frame 302 and holdthe shaft 360 in place within the channel 332. As noted above, theV-shaped portion 320 of the localization frame 302 forms an opening 368between its legs 322 and 324 so that the drill guide tube 364 may belocated therebetween and project downwardly from the plane generallydefined by the localization frame 302. This allows the surgeon to sightin the position of the drill guide tube 364 by looking through the tube.Connector 370 is similar to connector 340, except that it provides anangular engagement with the cable which allows for more freedom ofmovement of the localization drill guide assembly 350. As with thelocalization frame noted above, the frame itself is made of ULTEM 1000which is autoclavable. The handle may be wood, plastic, or any otherautoclavable material and the shaft, collar and drill guide may bemetal, plastic or other autoclavable material, such as stainless steel.FIG. 13K illustrates a preferred embodiment of the wiring diagram forthe localization drill guide assembly 350.

FIGS. 13F and 13G illustrate another localization device in the form ofa drill yoke localization frame 400. This frame 400 includes alocalization frame 302 of the same configuration as the localizationframes for the localization biopsy guide frame 300 and the localizationdrill guide assembly 350. Projecting from the underside of the baseplate 310 is a support member 402 which also supports a drill yoke 404in a plane which is essentially perpendicular to the plane defined bythe localization frame 302. Yoke 404 is essentially a collar which fitsover the housing of a Rex drill and is fixedly attached thereto by a setscrew 406. The drill yoke localization frame 400 allows the drillhousing to be precisely positioned for use during surgery.

Support member 402 also supports a connector 408 for receiving a cablewhich is connected to the digitizer control unit 114. Support member 402has a hollow channel therein so that the connector 408 may be connectedto the wires 410 which connect to the LEDs 316. FIG. 13J illustrates onepreferred embodiment of a wiring connection between the LEDs 316 and theconnector 408.

FIGS. 13H and 13I illustrate another localization device in the form ofa ventriculostomy probe 500. Probe 500 includes a handle 502 having abore 504 therein for receiving a support shaft 506 which in turnsupports a catheter guide tube 508 along an axis which is parallel tothe axis of the handle 502. The handle includes three LEDs 510 mountedalong its top surface for communication with the camera array 110. Thehandle 502 has a hollow channel terminating in a bore 512 for receivinga connector 514. The connector 514 is connected to wires 516 which arealso connected to the terminals of the LEDs 510. FIG. 13J illustratesone preferred embodiment of a wiring diagram for interconnecting theconnector 514 and the LEDs 510. In operation, the tube 508 is positionedwithin the body, the brain for example, so that a catheter may beinserted within the body. Tube 508 includes a top slot 518 which allowsa catheter to be inserted therein. Preferably, the tube tip at itscenter is collinear with the chip height of all three LEDs 510 so that alinear axis is defined therebetween. Based on this linear axis and thepredetermined knowledge of the distance between the tip and the LEDs510, the camera array 110 and digitizer 114 can determine the positionof the tip at any instant during a surgical or medical procedure.

The system of the invention may be used in the following manner. Areference frame is attached to a body part. For example, cranialreference arc frame 122 may be attached directly to a head via a headclamp such as a Mayfield clamp or spine reference arc frame 200 may beattached directly to a spinous bone via thoraco-lumbar mount 212.Thereafter, movement of the body part will result in correspondingmovement of the attached reference frame. The position of the body partmay be tracked by energizing the LEDs of the reference frame to providea signal to the camera array 110 so that the array can determine andtrack the position of the reference frame and, consequently, theposition of the body part.

A localization frame is used to precisely position an instrumentrelative to the body part. For example, a localization biopsy guideframe 300 may be used to position a biopsy needle relative to the bodypart. Alternatively, a localization drill guide assembly 350 may be usedto position a drill bit relative to the body part. Alternatively, adrill yoke localization frame 400 may be used to position a drillrelative to the body part. Alternatively, a ventriculostomy probe 500may be used to position a catheter relative to a body part. The positionof the instrument may be tracked by energizing the LEDs of thelocalization frame to provide a signal to the camera array 110 so thatthe array can determine and track the position of the localization frameand, consequently, the position of the instrument.

During calibration of the system, the position of the reference framerelative to the body part is determined. Markers used during thepreoperative scan are located and identified in coordinates of thesurgical space as defined by the reference frame. Note that anatomiclandmarks may be used as markers. This provides a relationship betweenthe preoperative scan space and the surgical space. Once thisrelationship is established, the system knows the position of thepreoperative scans relative to the reference frame and thus can generatescans which illustrate the position of the localization frame and theinstrument relative to the body part. In other words, the systemaccomplishes image guided surgery. The system is ideally suited forlocating small, deep-seated vascular lesions and tumors and for reducingthe extent of the microsurgical dissection. It is also useful inidentifying boundaries. For example, suppose a surgeon is trying toidentify a boundary between normal brain and large supratentorialgliomas, which may be clearly shown on the preoperative scans but whichmay be difficult to visually locate in the operating room during aprocedure. The surgeon would take a localization probe and position it apoint near the boundary. The LEDs of the reference frame andlocalization probe are fired by use of the foot switch 116. As a result,the monitor 106 would provide a screen showing the position of the proberelative to a preoperative scan. By referring to the monitor, thesurgeon can now determine the direction in which the probe should bemore to more precisely locate the boundary. One the boundary is located,microcottonoid markers can be placed at the boundary of the tumor asdisplayed on the monitor before resection is started. The placement ofventricular catheters for shunts, ventriculostomy, or reservoirs is alsofacilitated by the use of the system, especially in patients who havesmall ventricles or who have underlying coagulopatby (e.g., liverfailure, acquired immunodeficiency syndrome) that makes a single passdesirable. The system can also be useful for performing stereotacticbiopsies. For further information regarding the system, see thefollowing articles which are incorporated herein by reference in theirentirety: Germano, Isabelle M., The NeuroStation System forImage-Guided, Frameless Stereotaxy, Neurosurgery, Vol. 37, No. 2, August1995.

-   Smith et al., The Neurostation™-A Highly accurate, Minimally    Invasive Solution to Frameless Stereotactic Neurosurgery,    Computerized Medical Imaging and Graphics, Vol. 18, No. 4, pp.    247–256, 1994.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions, products,and methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above without departing from thescope of the invention, it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

1. A method for determining the geometry of a semi-rigid body elementduring a procedure, the method using an image data set having referencepoints for the body element, a relative position between said referencepoints of the semi-rigid body element being variable, the methodcomprising: identifying, during the procedure, the relative position ofeach of the reference points for the semi-rigid body element; deriving atransform relating the relative position of the reference points duringthe procedure to the relative position of the reference points in theimage data set in order to determine the geometry of the body elementduring the procedure, said transform indicative of a difference betweenthe relative position of each of the reference points for the semi-rigidbody element during the procedure and the relative position of thereference points in the image data set; modifying the image data setbased on the transform in order to generate a displaced image data setrepresenting the geometry of the body element during the procedure; andgenerating a display based on the displaced image data set illustratingthe geometry of the body element during the procedure.
 2. The method ofclaim 1 wherein the semi-rigid body element is soft tissue.
 3. Themethod of claim 1 wherein deriving comprises deriving a transformationwhich allows the determination of the procedural position, orientation,and shape in surgical space of the semi-rigid body element, and whereinmodifying comprises modifying the image data set according to saidtransfonnation to produce a displaced image data set reflecting changesin the geometry of the semi-rigid body elements during the procedure. 4.A method for determining the geometry and position of a semi-rigid bodyelement during a procedure, the method using a system including anarray, and instrument in communication with the array, and a processorin communication with the array and storing an image data set havingreference points for the body element, a relative position between saidreference points of the semi-rigid body element being variable, themethod comprising: touching the reference points for the semi-rigid bodyelement with the instrument during the procedure and communicating theposition of the reference points to the array; communicating theposition of the reference points of the body element during theprocedure to the processor; determining the relative position of thereference points; deriving a transform of the relative position of thereference points during the procedure to the relative position of thereference points in the image data set in order to determine thegeometry and position of the body element during the procedure, saidtransform indicative of a difference between the relative position ofeach of the reference points for the semi-rigid body element during theprocedure and the relative position of the reference points in the imagedata set; modifying the image data set based on the transform in orderto generate a displaced image data set representing the geometry andposition of the body element during the procedure; and displaying thegeometry and position of the body element during the procedure based onthe displaced image data set.
 5. The method of claim 4 wherein thesemi-rigid body element is soft tissue.
 6. The method of claim 4 whereinderiving comprises deriving a transformation which allows thedetermination of the procedural position, orientation, and shape insurgical space of the semi-rigid body element, and wherein modifyingcomprises modifying the image data set according to said transformationto produce a displaced image data set reflecting changes in the geometryof the semi-rigid body elements during the procedure.
 7. A system fordetermining the geometry and position of a semi-rigid body elementduring a procedure, the system comprising: an image data set of the bodyelement, the image data set having reference points for the bodyelement, a relative position between said reference points of thesemi-rigid body element being variable; an array of receivers; aninstrument in communication with the array, the instrument identifyingthe position of the reference points of the body element during theprocedure; a processor in communication with the array and storing theimage data set, the processor programmed to modify the image data setbased on the identified position of the reference points of the bodyelement during the procedure and to generate a displaced image data setrepresenting the geometry and position of the body element during theprocedure, said processor transforming the image data set indicative ofa difference between the relative position of each of the referencepoints for the semi-rigid body element during the procedure and therelative position of the reference points in the image data set; and adisplay for displaying the geometry and position of the body elementduring the procedure based on the displaced image data set generated bythe processor.
 8. The system of claim 7 wherein the processor derives atransformation which allows the determination of the proceduralposition, orientation, and shape in surgical space of the semi-rigidbody element, and wherein the processor modifies the image data setaccording to said transformation to produce a displaced image data setreflecting changes in the geometry of the semi-rigid body elementsduring the procedure.
 9. A system for determining the geometry andposition of a semi-rigid body element during a procedure, the systemcomprising: an image data set of the body element, the image data setdata points identifying a contour, said contour having a position andhaving contour reference points for the body element, a relativeposition between said reference points of the semi-rigid body elementbeing variable; an array of receivers; a scanning probe in communicationwith the array, the scanning probe determining the contour of the bodyelement during the procedure; a processor in communication with thearray and storing the image data set, the processor programmed todetermine the position of the contour of the body element during theprocedure and to compare the position of the contour of the body elementto the position of the contour of the body element as represented by theimage data set, the processor further programmed to modify the imagedata set based on the identified position of the contour of the bodyelement during the procedure and to generate a displaced image data setrepresenting the geometry and position of the body element during theprocedure, said processor transforming the image data set indicative ofa difference between the relative position of each of the referencepoints for the semi-rigid body element during the procedure and therelative position of the reference points in the image data set; and adisplay for displaying the geometry and position of the body elementduring the procedure based on the displaced image data set generated bythe processor.
 10. The system of claim 8, wherein the processor derivesa transformation which allows the determination of the proceduralposition, orientation, and shape in surgical space of the semi-rigidbody element, and wherein the processor modifies the image data setaccording to said transformation to produce a displaced image data setreflecting changes in the geometry of the semi-rigid body elementsduring the procedure.
 11. A method for determining the geometry of adeformable body element during a procedure, the body element havingreference points, the method comprising: obtaining an image data set ofthe deformable body element, the data set including the reference pointsfor the body element, a relative position between said reference pointsof the deformable body element being variable; identifying the relativeposition of each of the reference points for the body element during theprocedure; deriving a transform relating the relative position of thereference points during the procedure to the relative position of thereference points in the image data set in order to determine thegeometry of the body element during the procedure, said transformindicative of a difference between the relative position of each of thereference points for the semi-rigid body element during the procedureand the relative position of the reference points in the image data set;modifying the image data set based on the transform in order to generatea displaced image data set representing the geometry of the body elementduring the procedure; and generating a display based on the displacedimage data set illustrating the geometry of the body element during theprocedure.
 12. The method of claim 11 wherein the deformable bodyelement is soft tissue.
 13. The method of claim 11 wherein derivingcomprises deriving a transformation which allows the determination ofthe procedural position, orientation, and shape in surgical space of thesemi-rigid body element, and wherein modifying comprises modifying theimage data set according to said transformation to produce a displacedimage data set reflecting changes in the geometry of the semi-rigid bodyelements during the procedure.
 14. A system for use during a medical orsurgical procedure on a body, said system generating a displayrepresenting the position and geometry of a body element during theprocedure based on scans taken of the body by a scanner prior to theprocedure, the scan having reference points for the body element, arelative position between said reference points of the body elementbeing variable, and based on a position of a projection of the bodyelement prior to the procedure, said system comprising: means foridentifying, during the procedure the position of the reference pointsof the body element wherein said identifying means comprises a referencearray having a location outside the body for providing a reference,means for determining the position of the reference points of the bodyelement relative to the reference array, and a fluoroscopic device fordetermining a position of a projection of the body element during theprocedure; a processor comparing the position of the projection of thebody element during the procedure to the position of the projection ofthe body element prior to the procedure, said processor modifying theimage data set according to the comparison of the projection during theprocedure and the projection prior to the procedure and according to theidentified position of the reference points during the procedure, asidentified by the identifying means, said processor generating adisplaced image data set representing the position and geometry of thebody element during the procedure, said processor transforming the imagedata set indicative of a difference between the relative position ofeach of the reference points for the semi-rigid body element during theprocedure and the relative position of the reference points in the imagedata set; and a display utilizing the displaced image data set generatedby the processor, illustrating the position and geometry of the bodyelement during the procedure.
 15. The system of claim 14 wherein thefluoroscopic device comprises a fluoroscopic tube in fixed relation to afluoroscopic plate adapted so that the body element may be positionedtherebetween for determining a position of a projection of the bodyelement during the procedure and wherein the processor compares theposition of the projection of the body element during the procedure tothe position of the projection of the body element prior to theprocedure.
 16. The system of claim 15 wherein said fluoroscopic tube orsaid fluoroscopic plate each have emitters thereon in communication withthe reference array and wherein the determining means is adapted todetermine the position of the tube and plate relative to the referencearray whereby the position of the projection of the body element can bedetermined.
 17. The system of claim 15 wherein said reference array hasemitters thereon in communication with the fluoroscopic tube or thefluoroscopic plate and wherein the determining means is adapted todetermine the position of the tube or plate relative to the referencearray whereby the position of the projection of the body element can bedetermined.
 18. The system of claim 14 wherein the processor derives atransformation which allows the determination of the proceduralposition, orientation, and shape in surgical space of the semi-rigidbody element, and wherein the processor modifies the image data setaccording to said transformation to produce a displaced image data setreflecting changes in the geometry of the semi-rigid body elementsduring the procedure.